Hot cracking of slag pot

In the later stage of solidification, the solid phase has formed a complete skeleton and began to shrink linearly. If the linear shrinkage is hindered, cracks will occur in the slag pot. Because this kind of crack is formed at high temperature, it is called "hot crack". Hot cracking is one of the common casting defects in the production of steel castings, malleable iron castings and some light alloy slag pots.

(1) characteristics of hot cracking.

The hot crack is caused by the slag pot in the state of plastic deformation. because the slag pot is in the state of high temperature, the surface of the hot crack is oxidized seriously and has no metallic luster. For steel castings, the crack surface is approximately black, while the aluminum alloy is gray. When the cooling of steel castings is slow, decarburization still exists at the edge of the crack, and sometimes dendritic crystals can be found, and the hot cracks on the surface of the slag pot are wide and tearing. Another characteristic of hot crack is that the crack always occurs along the grain, which is significantly different from the cold crack.

The external crack in the hot crack can be seen on the surface of the slag pot, the crack starts from the surface of the slag pot, and gradually extends to the inside of the slag pot, and the crack sometimes crosses the whole section of the slag pot. The external crack often occurs at the corner of the slag pot, where the thickness of the section changes or where the local condensation is slow and easy to produce stress concentration, the main reason for the cracking of the slag pot is the tensile stress.

The internal crack in the hot crack usually occurs in the solidified part of the slag pot, and sometimes appears near or at the tail of the shrinkage hole, because the internal shrinkage hole is very irregular, there are often many crosses, and will not extend to the surface of the slag pot, so the degree of oxidation is not as obvious as the external crack.

Cracks are not allowed for any kind of slag pot, and the external cracks of the slag pot can be seen from the surface. If the cast alloy itself has good weldability, it can be used after welding repair. The welding performance is poor, and the slag pot is often scrapped. The internal crack is hidden inside the slag pot and is not easy to be found. its danger often causes serious accidents in use because it has not been discovered in advance. Therefore, enough attention should be paid to how to prevent hot cracks in the production process.